Polyaluminum chloride (PAC) is the name given to the family of compounds defined by the formula:Alm(OH)nCl3m-n 
Where 0<n≦3m and where m≧1. The degree of neutralization (i.e., the OH to Al ratio) is known as the basicity. In the case of polyaluminum chlorides the basicity is defined by the formula n/3m.
The solution chemistry of polyaluminum chlorides is complex. Although the formation of polynuclear aluminum species has been studied for over a century, there is still much controversy concerning aluminum polymerization reactions and the resulting product compositions. In general these materials are known to form a variety of oligomers and polymers in solution. Basicity is a major factor in determining the molecular species distribution; low-basicity favors low molecular weight species and high-basicity favors high molecular weight species. Temperature and concentration also effect the molecular species distribution but in less predictable ways.
PAC's can be broadly divided into three groups of basicities based on the manufacturing techniques used for their production. Low-basicity PAC with basicity from ˜1% to ˜45% is manufactured by the well known reaction of aluminum trihydrate (Al2O3—3H2O) with hydrochloric acid or aluminum chloride. High-basicity PAC with basicity of ˜45% to about ˜65% is manufactured by two methods. The first method known as the neutralization process relies on the reaction of aluminum chloride or low-basicity PAC with a base. The second method known as the oxidation process relies on the reaction of hydrochloric acid or aluminum chloride or low-basicity PAC with aluminum metal. And ultra high-basicity PAC (including ACH) with basicity of ˜65% to ˜83% is manufactured by the oxidation process (i.e., the reaction of hydrochloric acid or aluminum chloride or low-basicity PAC with aluminum metal). Based on these conventional processes for manufacturing PAC, high-basicity and ultra high-basicity products cost more to manufacture than low basicity products. The higher costs related to increased basicity is due to the relatively high cost of aluminum metal in comparison to other sources of aluminum (in the oxidation process) and the costs of acids and bases wasted in the neutralization process (vide infra).
Polyaluminum chlorides are used in diverse applications including catalysts, water treatment and antiperspirants. Each of these applications relies on the neutralization of PAC to form insoluble aluminum hydroxide. Although products with basicities ranging from ˜1% to ˜83% have commercial utility, the products with higher basicities generally have greater utility. Thus, catalyst applications favor PAC with basicity of ˜83%, antiperspirant applications favor basicities from ˜65% to ˜83% and water treatment applications favor PAC with basicities from ˜50% to ˜83%. The highest basicity PAC of commercial interest is the polyaluminum chloride with ˜83% basicity known as aluminum chlorohydrate (ACH); it has an empirical formula of Al2(OH)5Cl.
The challenges of satisfying the product requirements of these applications are many. In general, high concentration (i.e., high Al2O3 content) products are preferred when compared to low concentration counterparts. Thus catalyst applications require products with an Al2O3 content of ˜23.5% Al2O3. Antiperspirant applications frequently use dry products and processes which yield high Al2O3 content are desirable in order to minimize evaporation costs. In water treatment applications, PAC generally works more efficiently, produces less by-product sludge, settles faster, works better in cold water and reduces the pH of the water to a lesser extent than alternative products. In this application high-basicity PAC products with low Al2O3 content are generally favored. These product characteristics are common in water treatment because this product application can tolerate the presence of inert salts, and because this type of product can be economically manufactured by the neutralization process.
High-basicity (or ultra high-basicity) products are generally preferred in comparison to low-basicity products. And high Al2O3 content products are generally preferred in comparison to low Al2O3 content products. In many cases high-basicity (or ultra high-basicity) products with high Al2O3 content are preferred.
The reaction of aluminum chloride or hydrochloric acid with aluminum trihydrate used to manufacture low-basicity PAC has limited versatility. The reaction proceeds at elevated temperature and ambient pressure to produce products of modest basicity (<5% to 10%). Under moderate pressure, (up to 7 atm.) basicities of up to 40% to 45% are obtained. However, due to the corrosive nature of the reaction medium and the cost of operating at higher pressure, it is not practical to manufacture higher basicity products with this approach. PAC with forty-percent basicity is manufactured and sold commercially at a PAC concentration of about 36% (˜17.1% Al2O3).
The commercial process used for manufacturing high-basicity PAC, involves the neutralization reaction of aluminum chloride or low-basicity PAC with base and is shown below.
(In this reaction M+ is either an alkali ion, alkali earth ion or aluminum ion.) Processes which rely on bases (e.g. alkali hydroxides and/or carbonates, or alkali earth hydroxides and/or carbonates, or sodium aluminate) to produce higher basicity PAC's suffer from several limitations. The formation of salt (i.e., MCl) from the neutralization process limits the solubility and the stability of the products formed. Procedures for separating the high-basicity PAC from the salt, MCl, are not known. Therefore this procedure is unsuitable for making pure high-basicity PAC. Moreover, this approach is wasteful of raw materials (e.g., the hydrogen chloride and the base consumed in the neutralization process). Commercial products available by this route have low Al2O3 concentrations (less than 12.5% Al2O3 concentration is typical) due to the salt present from the neutralization process and have limited stability. Low concentration products are expensive to transport to end use customers.The waste of raw materials in the neutralization process is worthy of elaboration. The reaction of aluminum chloride with calcium carbonate is typical:
Aluminum chloride is manufactured by the reaction of hydrochloric acid with aluminum trihydrate. Thus, in the neutralization reaction above, four moles of hydrochloric acid and two moles of calcium carbonate are sacrificed in order to increase the basicity to 66%. In this example 1.15 lb of calcium chloride are produced for every pound of 66% basicity PAC produced. The raw material consumed by the neutralization process is wasteful and expensive. In addition, the calcium chloride generated in this process remains with the product thereby adding to overall solution concentration, and thereby reducing the solubility and stability of the PAC. The neutralization process has limited utility for manufacturing ultra high-basicity PAC due to the amount of co-product salt generated and the waste of raw materials.
High-basicity and ultra high-basicity PACs, including ACH are generally manufactured by the oxidation of aluminum metal in the presence of aluminum chloride, low basicity PAC or hydrochloric acid, the reaction below is typical.

This reaction yields high purity product because aluminum is readily available in high purity (99.7% and higher). This process is however not without limitations. Aluminum metal is expensive; on a contained aluminum basis, aluminum metal is two and a half to four times more expensive than the ATH used to manufacture low-basicity PAC's. The process is dangerous because hydrogen can undergo violent explosions. The reaction utilizes either, aluminum ingot, shot, or powder. Aluminum shot is more expensive than aluminum ingot, and powder is more expensive than shot. Aluminum ingot is slow to react and long batch times (up to 7 to 10 days) are common. Aluminum shot is easier to handle and somewhat more reactive (5 to 7 day reaction times are common), however the process is unpredictable; high turbidity batches requiring extensive settling and filtration are not uncommon. Aluminum powder gives faster reaction times (1 to 4 days depending on the size of the reaction), however powder requires special procedures due to its tendency to explode when exposed to air, static, or sparks.
Thus, more efficient processes are needed for manufacturing high-basicity PAC and ultra high-basicity PAC. Accordingly the present invention provides processes for manufacturing low-basicity, high-basicity and ultra high-basicity PAC products The processes of the present invention are not reliant on aluminum metal for producing ultra high-basicity products. The processes of the present invention provide highly efficient means for producing high-basicity products since the wasteful neutralization step practiced by conventional processes is eliminated.